1. Field of the Invention
The present invention relates to a chucking apparatus and its production method, and more particularly, to a chucking apparatus and its production method that is preferably used on the production lines of semiconductor devices such as IC, LSI and VLSI, and is capable of carrying out holding, alignment, transport and so forth of plate-shaped samples such as silicon wafers without causing problems such as the generation of particles.
2. Description of the Related Art
In the past, when performing holding, alignment, transport and so forth of plate-shaped samples such as silicon wafers, glass substrates and printed boards on the production lines of semiconductor devices such as IC, LSI and VLSI, the production lines of display devices such as liquid crystal displays (LCD) and plasma displays (PDP), and the assembly lines of hybrid ICs and so forth, chucking apparatuses were used that chucked and held these plate-shaped samples by electrostatic chuck systems or vacuum chuck systems.
A known example of a chucking apparatus used in the prior art is a chucking apparatus having a structure in which the upper surface of a base that chucks and clamps a plate-shaped sample is made to be an chucking surface, protrusions or grooves are formed in this chucking surface by sandblasting and so forth to form an irregular surface, and together with grinding the apices of the protrusions of this irregular surface to form a chucking surface for the plate-shaped sample, the indentations of this irregular surface are used as a supply path for a cooling gas such as helium (He).
In this type of chucking apparatus, lift pins for releasing the plate-shaped sample from the chucking surface are provided at locations on the back of the above base corresponding to the periphery of the plate-shaped sample.
In this type of chucking apparatus, adequate chucking force in terms of use is secured by making the contact surfaces with the plate-shaped sample (apices of the protrusions) into mirrored surfaces by polishing, and by making the total surface area of these contact surfaces within a prescribed range with respect to the chucking surface. In addition, by forming indentations in the chucking surface, the adherence of particles on the silicon wafer or other plate-shaped sample can be inhibited, and the plate-shaped sample can be easily released from the chucking surface. Moreover, by using these indentations as a supply path of a cooling gas such as helium, the plate-shaped sample can be cooled and controlled to a suitable temperature.
However, it is becoming necessary to provide the previously mentioned semiconductor devices of the prior art with higher levels of performance and at lower prices, and their production lines are being similarly required to offer further reductions in production costs by improving the production yield of silicon wafers and so forth. In addition, silicon wafers and other plate-shaped samples are being required to be free of adherence of particles more than in the past in order to improve the production yield of silicon wafers and so forth.
Therefore, as a result of conducting earnest studies in order to respond to these requirements, the inventors of the present invention found that the chucking apparatuses of the prior art had the problems indicated below.    (1) In the case of releasing a plate-shaped sample from the upper surface of the base by lifting the plate-shaped sample using lift pins, since this release takes place in a stepwise manner, there is contact between the back of the plate-shaped sample and the apices and sides of the protrusions of the chucking surface, causing rubbing of the back surface of the plate-shaped sample and resulting in the generation of particles.    (2) As shown in FIG. 6, when lift pins are raised to release a plate-shaped sample from the chucking surface of the base, since bending and other partial deformation occurs in plate-shaped sample 1 accompanying raising of the lift pins, the plate-shaped sample 1 is unable to be maintained parallel with respect to irregular surface 3 functioning as the chucking surface of chucking apparatus 2. As a result, the back of the plate-shaped sample 1 makes contact with and rubs against the bottom surfaces of the indentations of irregular surface 3 that have not been polished, resulting in the generation of particles. Furthermore, FIG. 6 shows an enlarged view of the length in the direction of thickness to facilitate understanding.